This invention relates to an apparatus and method for forming arcuate bends in round section metal tubing.
Round section metal tubing is manufactured from various materials and alloys in a variety of standardized sizes of nominal outside diameter and wall thickness, and is, generally, sold in straight lengths. Such tubing is widely used in many industries and trades, and, often, the terms "tube" and "pipe" are interchangeably used. While sections of tubing are available with preformed bends, such as "elbow sections" having a 90 degree bend, such preformed sections are expensive compared to straight sections and, additionally, such preformed bends as sold, are usually of a limited length. Therefore, preformed bends, typically, are joined to straight sections of tubing, which adds to the assembly costs. Thus, the need for a way to form bends in straight sections of round metal tubing has given rise to various types of apparatus. For example, such apparatus are often used in the manufacture of the preformed bend sections referred to above.
Due to the nature of the available types of round section-metal tubing, bends must typically be formed along a minimum inside bend-radius in order to avoid crimping the tubing. Furthermore, engineering practices prescribe minimum bend radii in order to assure the maintenance of adequate tube wall thickness and strength. Minimum radiuses are prescribed because the bending operation causes thinning by stretching the tube wall at the outer side of the bend and also by setting up compressive stresses in the tube wall at the inner side of the bend.
Various approaches have been taken in the art to avoid crimping the tube during bending, including the use of mandrel type devices placed inside the tube for supporting the tube wall. Examples of the use of mandrel devices for tube bending apparatus are found in U.S. Pat. Nos. 986,654 to Tattu, 1,007,834 to Wilson and 1,600,339 to Klarwasser. However, the use of mandrels is often impractical, and undesirably adds complexity to the bending operation, especially where a bend is to be formed at a distance from the open ends of a tube.
In order to assure a uniform minimum bending-radius, there have been employed various types of components known as "radius blocks", "bending shoes", and "bending dies". All of these components are generally characterized by having a curved, hemispherical, or semicircular section-die concavity formed therein along a desired radius, where the concavity of the die's cross-section conforms to the outer diameter of the tube to be bent. By various means, the tube is forced to engage and follow the concavity in the radius block's bending die along its curvature, in which way the tube is caused to be formed with the desired bend radius. Typically, such radius blocks may be mounted for rotation about an axis, which axis thus becomes the centerline of the bend radius. In such a typical apparatus, the tube to be bent may be held in place against the concavity of the radius block's curved die at the beginning or starting location of the bend by means of a clamping device, so that as the radius block is caused to rotate about its axis, the tube, being clamped to the radius block, is forced into the curved concavity of the radiused die. In order to assure that the tube is fed into the curved concavity of the radius block die as the radius block is rotated about its axis, and also in order to prevent undesirable bulging or narrowing of the tube cross-section at the bend location, known apparatus also typically employ a component known variously as a "slide block", "follow block", "backing block" or "backing die" which is formed with a hemispherical or semicircular section concavity therein conforming to the tubing outside diameter in the manner of the radius block's bending die, but such slide blocks are straight rather than curved and the concavity therein is also straight. Such slide blocks are typically movable longitudinally along their axis of concavity, i.e., in a direction parallel to the straight axis of the tubing. In this manner, the slide block is made to lie snugly against the outside portion of the tube in opposition to the curved radius block die, with the outside portion of the tube being thus engaged within the concavity of the slide block. Then, as the radius block, having the starting tube section clamped thereto, is rotated about its axis, the tube's straight following inside portion is "pulled" or drawn by its clamped straight starting section into engagement with the curved following concavity of the radius block die causing a bend to be started in the tube, while the tube's corresponding opposing following outside portion, which had been previously engaged within the straight concavity of the slide block is caused to be drawn inwardly toward the radius block's curved die and away from and out of engagement with the straight concavity of the slide block. At the same time, because of the snug fit between the outer tube portion and the concavity of the movable slide block, the slide block is drawn forward by the tube as the tube is drawn onto the radius block's bending die, causing the slide block to move tangentially in relation to the curvature of the radius bend being formed in the tubing. As the radius block is rotated further, the following straight inside portions of the tube are continuously and successively drawn into engagement with the corresponding following portions of the curved concavity of the radius block's bending die while the corresponding following outside portions of the tube are correspondingly continuously and successively drawn away from and out of engagement with the opposing straight concavity of the slide block. In this way, as long as the radius of curvature of the radius block's bending die concavity is not below the minimum bend radius, then the round cross-section of the tubing can be substantially maintained during the bending operation and crimping of the tubing avoided.
In the operation of such a typical apparatus, tube bending is thus performed by rotating the radius block the desired number of degrees to produce a bend of a corresponding number of degrees.
Exemplifying typical apparatus for forming radiused tubing bends in this manner are U.S. Pat. Nos. 986,654 to Tattu, 1,007,834 to Wilson, and 3,546,917 to Paine.
Other conventional tube bending apparatus are disclosed by U.S. Pat. Nos. 118,847 to Doe, 1,662,131 to Schonfield, 2,782,832 to Shaw, Jr. and 4,537,052 to Adelman.
Another typical tube bending apparatus in commercial use which employs a rotatable radius block and an opposing movable slide block is the Model HB832A tube bender manufactured by the Lakeland Products division of Teledyne Republic of Cleveland, Ohio. In this apparatus, interchangeable radius, clamp and slide blocks allow tubing of various diameters to be bent. The radius block around which the tube is bent is driven by a roller chain and sprocket, which rotates the center post and drive plate upon which the radius block is mounted. The roller chain is secured at its one end to the piston rod of a hydraulic cylinder, and thus hydraulic pressure is utilized in this apparatus to move the roller chain, which, being wrapped around the center post's sprocket, translates the linear motion of the piston into rotary motion of the sprocket and center post thus rotating the drive plate and radius block.
However, this reliance upon hydraulic power is disadvantageous in that a cumbersome external source of hydraulic power such as an electrically powered pump is required, which must be disconnected from and reconnected to the bender unit every time the unit is moved to a new site. Still further, this reliance upon hydraulic power gives rise to the serious possibility of a tube being bent becoming contaminated with hydraulic fluid due to leaking seals and couplings, burst hoses, spillage or carelessness. Such possibility of contamination can be hazardous where the tubing is to be used in or exposed to a nitric acid environment, due to the nitratability of commonly used hydraulic fluids, which can produce a crude form of explosive nitroglycerin. Cleanliness is also of prime concern in the food and drug industry.
A further drawback in the suitability of this apparatus results from its inability to perform bends in tubing having a wall thickness greater than 0.120 inch. Additionally, this apparatus suffers the shortcoming of being limited to effecting maximum bends of only 180 degrees. Also, because the roller chain is tensioned at its end opposite the hydraulic cylinder's piston by a spring in order to return the mechanism to a 0 degree starting position after a bend is completed, it is possible that the radius block's rotational direction may become reversed, as upon the sudden loss or releasing of hydraulic pressure, thus risking wrinkling or crimping of the tube.
Another problem encountered in the use of the conventional tube bending apparatus involves the complexity of gauging or laying out the center to center dimensions of finished bends. In particular, due to the radial deflection of the tube's centerline along the direction of the bend during the bending operation, it is difficult to accurately gauge the center to center dimensions of the finished bend. This "gain" is an inherent result of the bending process, yet the conventional tube bending machines make no provision for gauging the "gain" involved in forming a tubing bend. Rather, the conventional machines provide only sundry means for gauging the radius and degree sweep of a bend, and it is thus left to the artisan to gauge the center to center dimension of a finished bend. The need for accurate gauging becomes important when producing bend sections which must align precisely with a centerline, and when compound and reverse bends must be precisely formed in a tube.
In order to remedy the problems encountered in conventional tube benders, the present invention provides a tube bending apparatus of simple yet sturdy design incorporating significant design improvements, operational advantages and expanded capabilities over conventional designs. The present tube bending apparatus employs interchangeable rotatable radius block means to which a tube may be clamped with tube clamping means, and interchangeable slide block means for supporting a tube during bending. Adjustable slide block retaining means are provided for proper positioning of the slide block means. One-way drive means are provided for one-directional rotation of the radius block means during the bending operation in order to prevent reverse rotational driving of the radius block means for improved safety, and to permit driving of the apparatus by either portable electrically powered or manual driving means. Means are also provided for selectively disengaging the driveline to permit freewheeling of the radius block means. The one-way drive means is capable of drivingly rotating the radius block means an unlimited number of degrees in the bending direction. In a second embodiment of the present invention, novel radius block means and slide block means are provided for forming overlapping radiused 360 degree tube bends. Further, the present invention provides a method and means for accurately gauging the finished center to center dimensions of bends before commencing a bending operation, for facilitating the laying out of precise bends.
The present invention is directed to overcoming the above-mentioned limitations of the conventional tube bending machines by providing a portable tube bending apparatus which may be operated manually or with a widely used portable electrically driven power unit.
The present invention is further directed to overcoming the limitations of the conventional tube bending machines by providing a tube bending apparatus which is capable of forming radiused bends in thin, medium and thick walled round section metal tubing.
The present invention is still further directed to overcoming the limitations of the conventional tube bending machines by providing a method for forming radiused 360 degree bends, and by providing a tube bending apparatus which is capable of forming 360 degree radiused bends in round section metal tubing.
The present invention is further still directed to overcoming the limitations of the conventional tube bending machines by providing a tube bending apparatus having safety interlock means for preventing rotation of the radius block in the wrong direction.
The present invention is yet further directed to overcoming the limitations of the conventional tube bending methods and machines by providing a method for forming radiused bends having accurate center to center dimensions, and furthermore, by providing a tube bending apparatus including means for forming radiused bends with accurate center to center dimensions.
These and other objects and advantages of the present invention will be made clear from the following detailed description of the invention taken together with the drawing figures, in which like-numbered elements among the various figures correspond to one another.